Breast Microbiota and Breast Cancer: Current Evidence and Clinical Implications

Abstract

Breast microbiota refers to the microorganisms living in breast tissue, and current research focuses on the changes in this microbial community that influence breast cancer development in accordance with breast microbiota and its relation to cancer, and relevant biomarkers. Breast cancer remains the most frequently diagnosed malignancy among women worldwide and is a leading cause of cancer-related mortality. While genetic, hormonal, and environmental factors have long been recognized as key contributors to breast carcinogenesis, growing evidence highlights the breast microbiota as a potential modulator of breast health and disease. Once considered sterile, the breast tissue is now known to harbor a diverse microbial community comprising bacteria, fungi, viruses, and other microorganisms that interact with the host immune system and local tissue microenvironment. Alterations in the composition and diversity of this microbial ecosystem commonly referred to as dysbiosis, have been associated with breast cancer initiation, progression, metastasis, and response to therapy. Emerging studies have identified distinct microbial signatures in healthy and malignant breast tissues, suggesting that specific microbial taxa may influence carcinogenesis through mechanisms including chronic inflammation, immune modulation, estrogen metabolism, DNA damage, and the production of microbial metabolites. Furthermore, advances in high-throughput sequencing and multi-omics technologies have expanded our understanding of host–microbe interactions and their potential role in precision oncology. This review summarizes current knowledge on the composition of the breast microbiota, its proposed mechanisms in breast cancer development, and the differences observed across breast cancer subtypes. It also discusses the influence of microbiota on therapeutic efficacy and treatment-associated toxicity, as well as the emerging potential of microbiome-based biomarkers and interventions, including probiotics, prebiotics, and microbiota modulation strategies. Despite promising findings, significant challenges remain regarding methodological standardization, causality, and clinical translation. Continued research is essential to elucidate the functional role of the breast microbiota and to establish its utility as a diagnostic, prognostic, and therapeutic target in breast cancer management.

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